Why does the M stay on my Nikon SB-600 flash?

I'm using a nikon sb-600 flash for my camera. Can someone tell me how I can remove the M from the display? The zoom on the display used to work instantly as I zoomed in and out on the camera, and there was no M shown. Also, it will only display TTL, and BL does not show up any more. Can someone tell me why this happened and how I can change it back?

Added (1). Mine must be broke then… When i hit mode, all it does is cycle through, and never shows BL… All i can think of is must be some problem with connection to the camera, since i tried the flash on my other camera and its doing same thing, even after resetting 5 times

Each time you depress the MODE button, it should change from M (manual), TTL (iTTL), or TTL BL (iTTL with fill flash balance).

The second M to the lower left is for the zoom, and whether it is in manual zoom mode or not. That is changed with the ZOOM button.

If that all fails, you can reset the flash by depressing the MODE and POWER buttons and hold them for 2 seconds.

If none of the above works, make sure you have not locked the controls. If they are locked, there will be a little padlock icon on the display. To fix that, depress the MODE and (MINUS) buttons simultaneously for 2 seconds. Each time you depress those two buttons the lock toggles on and off.

There's also a power zoom on-off custom setting that disables the zoom head function - see page 53 in your manual.

The SB600 is not really that intuitive to use. I have one, and I'm upgrading to a SB700 as I have to look at the manual almost constantly.

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